The IEEE 802.11 WLAN standard provides a number of physical layer options in terms of data rates, modulation types and spreading spectrum technologies. An extension of the IEEE 802.11 standard, namely IEEE 802.11a, defines requirements for a physical layer operating in the 5 GHz U-NII frequency and data rates ranging from 6 Mps to 54 Mps. IEEE 802.11a defines a physical layer based on the orthogonal frequency division multiplexing (OFDM). This physical layer is similar to the one defined by the European ETSI-HIPERLAN II (European Telecommunications Standards Institute-HiperLAN2). A second extension, IEEE 802.11b, defines a set of physical layers' specifications operating in the 2.4 GHz ISM frequency band up to 11 Mps. The direct sequence spread spectrum/complementary code keying (DSSS/CCK) physical layer is one of the three physical layers supported in the IEEE 802.11 standard and uses the 2.4 GHz frequency band as the RF transmission media.
The IEEE standard committee has created a working group TGg with the mission of developing a higher speed PHY extension to the 802.11b standard. The 802.11g standard will be compatible with the IEEE 802.11 MAC and will implement all mandatory portions of the IEEE 802.11b PHY standard. A scope of TGg is to provide a wireless LAN standard where stations communicating in OFDM modulation and legacy stations communicating in DSSS/CCK modulation coexist and communicate with each other.
Another extension IEEE 802.11e enhances the current 802.11 MAC to expand support for LAN applications with Quality of Service requirements. IEEE 802.11e enables direct communications from one station to another. Example applications include transport of voice, audio and video over 802.11 wireless networks, video conferencing, media stream distribution, enhanced security applications, and mobile and nomadic access applications.